Catalyst for Benzene Hydroxylation for Preparation of Phenol and Preparation Method Thereof

ABSTRACT

The invention relates to a catalyst for benzene hydroxylation for preparation of phenol and a preparation method thereof, wherein said catalyst uses a mesoporous material as carrier, and the catalyst is prepared by first modifying the surface of the carrier using aminosilane, then immersing with acetylacetonate salt of metal, and finally washing and drying. Advantage of the invention is that a reactive metal is loaded on the silane-modified mesoporous material to form a homogeneous-heterogeneous composite catalyst, wherein, the reactive metal component is present in a reaction system in a homogeneous form, which ensures high catalytic performance of the catalyst component, and it is loaded on the carrier through bridging action of aminosilane, which improves the acting force between the metal component and the carrier, enhances stability of the catalyst, and facilitates separation of the catalyst from the product. The catalyst has a simple preparation process, has excellent catalytic performance, and can be applied to the reaction system of benzene hydroxylation for preparation of phenol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from CN Application No. 201310474635.0, filed Oct. 11, 2013 and PCT Application No. PCT/CN2014/086353, filed Sep. 12, 2014, the contents of which are incorporated herein in the entirety by reference.

TECHNICAL FIELD

The invention relates to a preparation method of homogeneous-heterogeneous composite catalyst, in particular to catalyst for benzene hydroxylation for preparation of phenol and preparation method thereof, and belongs to the field of catalysis technique.

BACKGROUND OF THE INVENTION

Phenol is an important organic chemical raw material, mainly used for production of phenolic resin, bisphenol A, epoxy resin, caprolactam and aniline, and also has wide applications in synthetic fiber, synthetic rubber, plastic, medicine, pesticide, flavor, dye, paint and the like. Now in the world, the industrial production of phenol is mainly realized through the cumene method. This process has high energy consumption, and low phenol yield and produces a large amount of co-product acetone at the same time, and a plurality of organic reagents are to be added into the reaction, which causes resource wasting, inconvenient operation and serious environment pollution. In recent years, synthesis of phenol in one step by direct benzene hydroxylation becomes a research hot spot. This method has simple process, little environment pollution and other characteristics, is an environmental-friendly catalytic process, and has very wide prospects of industrial development and application.

Oxidant used for direct catalytic oxidation of benzene for preparation of phenol generally comprises oxygen, N₂O and H₂O₂. Oxygen has extensive sources, and low cost, therefore, preparation of phenol by direct oxidation of benzene with oxygen as oxidant is the way with the most development value and application prospect. At present, the method for preparation of phenol by oxidation of benzene with oxygen mainly includes a gas phase method and a liquid phase method. The gas phase method is a high-temperature reaction, and problems such as catalyst deactivation and deep product oxidization easily occurs during the reaction process. The liquid phase method has a relatively low reaction temperature, and a mild reaction condition, and attracts broad attention. The key of the liquid phase method is to design a catalyst for activating oxygen molecules. The reactive component of the catalyst is generally metal, for example copper, vanadium, palladium, and iron. In the reaction process, loss of the metal component of the catalyst is the bottleneck problem to restrict the application of such catalyst. Therefore, development of high-performance catalyst is the focus of studying the process for preparation of phenol by benzene hydroxylation.

At present, the catalysts disclosed in the existing patents are mainly supported catalyst, the carriers used are mainly SiO₂, C or Al₂O₃, the reactive components are mainly palladium, platinum, copper, vanadium, iron or zinc, and the preparation of supported catalyst are mentioned in Patents CN1102452901A and CN102463124A, and used for preparation of phenol by benzene hydroxylation. Preparation of these catalyst generally requires calcination and has high preparation cost. And in the reaction process, the metal component is dissolved and then lost into the reaction solution, which leads to loss and activity decrease of catalyst, and also affects purity of products.

SUMMARY OF THE INVENTION

An objective of the invention is to overcome the problem of easy loss and poor stability of the existing catalyst for benzene hydroxylation for preparation of phenol in the reaction system, and provide a catalyst for benzene hydroxylation for preparation of phenol, and another objective of the invention is to provide a preparation method of above catalyst, link the reactive component of the catalyst to carrier through aminosilane to form a homogeneous-heterogeneous composite catalyst, enhance the acting force between the reactive component and the carrier, and improve catalytic performance of the catalyst.

Technical scheme of the invention is as follows: the mesoporous material is used as carrier; its channel surface is functionalized using aminosilane, then the reactive component is loaded onto the aminosilane-modified mesoporous material through an immersion method to prepare a homogeneous-heterogeneous composite catalyst with high performance. Aminosilane (such as Δ-aminopropyltriethoxysilane KH550) has two functional groups, one functional group alkoxy can be condensed with hydroxyl on the surface of the mesoporous carrier to form a chemical bond such as Si—O—Si or Al—O—Si, and the other functional group —NH₂ has a pair of lone pair electrons, and can form a coordination bond with metal ions, and firmly adsorb the reactive metal component. As a result, functionally modifying the carrier surface with aminosilane such as KH550 and then loading the reactive metal component onto the modified carrier can realize compounding of the homogeneous catalytic reactive component and the heterogeneous carrier, wherein, reactive metal component is present in the reaction system in a homogeneous form, which ensures high catalytic performance of the catalyst component, and it is loaded on the carrier through bridging action of aminosilane, which facilitates separation of the catalyst from the product, and the catalyst can still keep good catalytic performance after repeated use.

The specific technical scheme of the invention is: a catalyst for benzene hydroxylation for preparation of phenol, wherein: with a mesoporous material SBA-15, SBA-16 or MCM-41 with its channel surface functionally modified using aminosilane as carrier, and with palladium, platinum, copper, vanadium, iron or zinc as a reactive component, a homogeneous-heterogeneous composite catalyst is prepared by loading the reactive component onto the aminosilane-modified mesoporous material through an immersion method, wherein, the reactive metal component is loaded onto the carrier through bridging action of aminosilane, which improves the acting force between the metal component and the carrier, enhances stability of the catalyst, and facilitates separation of the catalyst from the product; and the reactive metal component is present in a reaction system in a homogeneous form, which ensures high catalytic performance of the catalyst component. Preferably the reactive component is copper or vanadium.

The invention also provides a method for preparing the above catalyst, and the specific steps are:

A. carrier surface modification process: immersing the carrier into aminosilane solution with a concentration of 0.1-2 g/L, performing surface modification at a temperature of 20-40° C., taking out, washing and air drying;

B. immersion process: immersing the modified carrier into acetylacetonate solution containing reactive components such as palladium, platinum, copper, vanadium, iron or zinc, immersing at a temperature of 20-40° C. for 6-36 h; wherein the immersion solution has a concentration of 0.1-0.25 mol/L; and

C. washing and drying process: washing the catalyst with absolute ethanol or dichloromethane and drying.

Preferably in the step A the aminosilane is γ-aminopropyltriethoxysilane (KH550) or N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH792) or N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (silane coupling agent 602); the solvent is dichloromethane, toluene or absolute ethanol; and the modification time is 1-32 h.

The invention employs the following conditions to perform activity evaluation of the catalyst.

Reaction is performed in 150 ml three-neck flask. 40 ml of glacial acetic acid, 10 ml of distilled water, 2 g of benzene, 4 g of ascorbic acid and 0.5 g of catalyst are added into the reaction flask sequentially, the inlet oxygen flow is adjusted to 30 ml/min, the temperature is controlled constant at 30° C., sample is collected after 6 h of reaction, the product is analyzed by high performance liquid chromatography, and benzene conversion and phenol selectivity are calculated according to a standard curve.

Beneficial Effects:

In the invention the reactive component is loaded onto the aminosilane-modified mesoporous material through an immersion method to form a homogeneous-heterogeneous composite catalyst, wherein, the reactive metal component is present in the reaction system in a homogeneous form, which ensures high catalytic performance of the catalyst component, and it is loaded on the carrier through bridging action of aminosilane, which facilitates separation of the catalyst from the product, and the catalyst can still keep good catalytic performance after repeated use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is X-ray diffraction diagrams of SBA-15 carrier, V/NH2-SBA-15 (Example 1) catalyst and vanadiumoxy acetylacetonate (VO(C₅H₇O₂)₂) precursor.

FIG. 2 is infrared characterization diagrams of SBA-15, NH2-SBA-15 (Example 1), VO(C₅H₇O₂)₂ and V/NH₂-SBA-15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Effects of the catalyst and the preparation method of the invention are further illustrated below through Examples.

EXAMPLE 1 Preparation of V/NH₂-SBA-15 Catalyst

2 g of SBA-15 is dispersed in 50 ml of dichloromethane solvent, and 0.05 g of aminosilane KH550 is added, stirred at 25° C., immersed for 1 h, washed with absolute ethanol, filtered and then dried to obtain NH₂-SBA-15 powder. 1.33 g of VO(C₅H₇O₂)₂ (molecular weight of 265.15) is added to 50 ml of CH₂Cl₂, and stirred, and after the solid is completely dissolved, 1.5 g of NH₂-SBA-15 powder is added, stirred at 40° C., filtered after 12 h of immersion, washed with absolute ethanol, and dried at 90° C. to obtain V/NH₂-SBA-15 catalyst.

FIG. 1 shows the analysis result of X-ray diffraction of the V/NH₂-SBA-15 catalyst. SBA-15 has a strong peak at 22°, corresponding to amorphous Si. V/NH₂-SBA-15 presents characteristic peaks of VO(C₅H₇O₂)₂ and Si, which indicates that the catalyst component has been loaded on the SBA-15 carrier.

From FIG. 2, 960 cm⁻¹ corresponds to Si—OH, the strength of V/NH₂-SBA-15 significantly decreases at 960 cm⁻¹, and this is due to silane functionalization of the carrier and loading of VO(C₅H₇O₂)₂. Furthermore, it can be found by comparing c and a that there are additional two peaks at 2930 and 2848 cm⁻¹, which correspond to C—H stretching vibration, while 1557 cm⁻¹ corresponds to bending vibration, which indicates that silane is grafted onto the surface of SBA-15 through a chemical bond.

The catalyst is used in a system for preparation of phenol by benzene hydroxylation, and after 6 h of reaction, the yield of phenol is 4.5%. After the catalyst is used for 5 times, the catalytic efficiency is reduced to 70% of that of fresh catalyst.

EXAMPLE 2 Preparation of V/NH₂-MCM-41 Catalyst

2 g of SBA-15 is dispersed in 50 ml of dichloromethane solvent, and 0.1 g of aminosilane KH792 is added, stirred at 20° C., immersed for 8 h, washed with absolute ethanol, filtered and then dried to obtain NH₂-MCM-41 powder. 3.31 g of VO(C₅H₇O₂)₂ (molecular weight of 265.15) is added to 50 ml of CH₂Cl₂, and stirred, and after the solid is completely dissolved, 1.5 g of NH₂-SBA-15 powder is added, stirred at 20° C., filtered after 6 h immersion, washed with absolute ethanol, and dried at 90° C. to obtain V/NH₂-MCM-41 catalyst.

The catalyst is used in a system for preparation of phenol by benzene hydroxylation, and after 6 h of reaction, the yield of phenol is 3.9%. After the catalyst is used for 5 times, the catalytic efficiency is reduced to 62% of that of fresh catalyst.

EXAMPLE 3 Preparation of Pd/NH₂-SBA-15 Catalyst

2 g of SBA-15 is dispersed in 50 ml of dichloromethane solvent, and 0.05 g of aminosilane KH550 is added, stirred at 40° C., immersed for 24 h, washed with absolute ethanol, filtered and then dried to obtain NH₂-SBA-15 powder. 3.05 g of Pd(C₅H₇O₂)₂ (molecular weight of 304.64) is added to 50 ml of CH₂Cl₂, and stirred, and after the solid is completely dissolved, 1.5 g of NH₂-SBA-15 powder is added, stirred at 40° C., filtered after 36 h of immersion, washed with absolute ethanol, and dried at 90° C. to obtain Pd/NH₂-SBA-15 catalyst.

The catalyst is used in a system for preparation of phenol by benzene hydroxylation, and after 6 h of reaction, the yield of phenol is 2.5%. After the catalyst is used for 5 times, the catalytic efficiency is reduced to 60% of that of fresh catalyst.

EXAMPLE 4 Preparation of Cu/NH₂-SBA-16 Catalyst

2 g of SBA-15 is dispersed in 50 ml of dichloromethane solvent, and 0.005 g of silane coupling agent 602 is added, stirred at 30° C., immersed for 32 h, washed with absolute ethanol, filtered and then dried to obtain NH₂-SBA-16 powder. 1.96 g of Cu(C₅H₇O₂)₂ (molecular weight of 261.76) is added to 50 ml of CH₂Cl₂, and stirred, and after the solid is completely dissolved, 1.5 g of NH₂-SBA-16 powder is added, stirred at 25° C., filtered after 12 h of immersion, washed with absolute ethanol, and dried at 90° C. to obtain Cu/NH₂-SBA-16 catalyst.

The catalyst is used in a system for preparation of phenol by benzene hydroxylation, and after 6 h of reaction, the yield of phenol is 3.1%. After the catalyst is used for 5 times, the catalytic efficiency is reduced to 65% of that of fresh catalyst. 

What is claimed is:
 1. A catalyst for benzene hydroxylation for preparation of phenol, wherein: with a mesoporous material SBA-15, SBA-16 or MCM-41 with its channel surface functionally modified using aminosilane as carrier, and with palladium, platinum, copper, vanadium, iron or zinc as a reactive component, a homogeneous-heterogeneous composite catalyst is prepared by loading the reactive component onto the aminosilane-modified mesoporous material through an immersion method, wherein, the reactive component is loaded onto the carrier through bridging action of aminosilane.
 2. The catalyst according to claim 1, wherein the reactive component is copper or vanadium.
 3. A method for preparing the catalyst according to claim 1, the specific steps are: A. carrier surface modification process: immersing the carrier into aminosilane solution with a concentration of 0.1-2 g/L, performing surface modification at a temperature of 20-40° C., taking out, washing and air drying; B. immersion process: immersing the modified carrier into acetylacetonate solution containing reactive components such as palladium, platinum, copper, vanadium, iron or zinc, immersing at a temperature of 20-40° C. for 6-36 h; wherein the immersion solution has a concentration of 0.1-0.25 mol/L; and C. washing and drying process: washing the catalyst with absolute ethanol or dichloromethane and drying.
 4. The preparation method according to claim 3, wherein in the step A the aminosilane is γ-aminopropyltriethoxysilane (KH550) or N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH792) or N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (silane coupling agent 602); the solvent is dichloromethane, toluene or absolute ethanol; and the modification time is 1-32 h. 